The capacity of a cellular system operating with a multi-path channel can be limited by a demodulator's ability to mitigate the degradations of the received signal due to the multi-path channel. One receiver known in the art for receiving coded transmissions over a multi-path channel is a maximum likelihood sequence estimator (“MLSE”) that operates to jointly demodulate the channel and the error correction code. However, the complexity of an MLSE is proportional to PL+K, where P is the number of points in a signal constellation, K is the number of stages in a convolutional code shift register, and L is the number of symbol spaced taps of the multi-path channel. Such complexity impedes an implementation of the MLSE into a cellular system.
Another known receiver for receiving coded transmissions over a multi-path channel is a turbo decision-feedback equalizer (“TDFE”) having feed-forward filters and feedback filters that are based upon an estimation of the multi-path channel. While the complexity of the TDFE does not impede the implementation of the TDFE into a cellular system, a problem with the TDFE is the computation of the filters assumes perfect feedback that is not attained in practice.
Therefore, there is a need for an adaptive TDFE. The present invention addresses this need.